The present invention relates to a material having a damping property and masterbatch pellets used for production thereof. More particularly, the present invention relates to a material having a damping property which shows a high internal loss at around room temperature and has a sufficient strength and hardness. The material having a damping property (hereinafter referred to as "damping material") of the present invention is mainly used as structural materials of electrical or electronic equipments, casings or bodices of household electric appliances of office automation equipments, parts of various kinds of machines and apparatus, interior parts of vehicles and ships, building materials and the like. It finds particularly useful application to a cartridge half and a cassette half.
As is well known, a damping material is widely used in many fields of industry for the purpose of damping vibration or noise generated from various sources and occasions, for example, vibration or noise which is generated incidental to operation of engine or motor mounted in various kinds of machines and apparatus, for instance, office automation equipments, household electric appliances such as washing machines, dryer, etc., a cartridge half and cassette half of data cartridge tapes, video tapes, audio tapes, etc., disk shells of optical discs, magneto-optical discs, magnetic discs, acoustic optical discs, etc., acoustic equipments, precision machine tools, works plant equipments, and various kinds of vehicles and ships; vibration or noise generated from piping such as water and gas pipes in buildings, ducts of air conditioning systems, etc.; and vibration or noise generated from running of vehicles on road or railway tracks.
The damping material is usually offered as a sheet-like material or block-like material produced by kneading and molding a binder resin and filler material such as mica, iron oxide or the like by a suitable molding method such as extrusion molding, calender molding, compression molding, injection molding or cast molding, or it is provided directly as a structural material of electrical or electronic equipments, casings of household electric appliances, office automation equipments, a cartridge half and a cassette half, etc. Namely, as for the using mode of the damping material, it may be used so that a molded sheet-like material or block-like material is stuck to or put between pertinent section(s) of an objective apparatus, etc., or it may be directly applied as a structural material of electrical or electronic equipments, casings of household electric appliances, office automation equipments, a cartridge half, a cassette half, etc.
Recently, there is seen a remarkable trend toward the miniaturization and lightweight of handy apparatus such as office automation equipments and acoustic equipments, and a damping material used in such machines, equipments, appliances and tools has been strongly required to miniaturize and reduce the weight. To meet this requirements, the damping material is demanded to have a high damping property, that is, a high internal loss. However, if it is simply tried to increase the amount of inorganic filler material used in the damping material for the only purpose of improving damping property, it invites a reduction of strength and hardness of rigid resin used as binder resin, and moldability of the material is impaired. Further, since specific gravity of the produced damping material elevates, this runs counter to the requirements of the miniaturization and lightweight. It is thus strongly required of damping material to have an excellent damping property while maintaining an intrinsic strength (e.g. bending strength) and hardness of a rigid resin. This fact is referred to in, for instance, Japanese Patent Application Laid-open (KOKAI) No. 4-45142 which states: "As thermoplastic resin composition having damping properties, there are known compositions obtained by blending a large amount of filler material such as calcium carbonate with polypropylene. These compositions, however, had the disadvantages in that the intrinsic priorities of resin (such as good moldability and high impact strength) are deteriorated because of blending of a large amount of filler material. Development of a damping materiel capable of retaining the intrinsic properties of resin has, therefore, been desired."
Recently, large numbers of the movable parts such as motors, relays, transforms, gears, cums, gear boxes and the like, and the electrical, electronic or machine parts which generate vibration and/or noise are used in the household electric appliances or the office automation equipments. The vibration generated from such parts is transferred to other parts and/or casings, and as a result, the intended performances of the product can not be exhibited. According to circumstances, it may be invite to malfunction and/or generate unpleasant vibration. So, the damping material used as a structural material of the electrical, electronic or machine parts, and the casings of the household electric appliances or the office automation equipments is strongly required to have a sufficiently high strength and hardness, and excellent internal loss at around room temperature (e. g., 20 to 28.degree. C.).
Also, in recording media such as optical disks or magnetic disks used in computers, word processors and the like, data-cartridge tapes, video and audio optical disks, cassette tapes, etc., higher reliability, tone quality and picture quality of the recording media are strongly demanded.
These recording media are set in a recorder and driven to run by a motor or other motive force to make recording or reading-out. Vibration generated in the inside of the cartridge half or cassette half (for example, vibration caused by "play" around a shaft such as hub for taking up the magnetic tape) or vibration from a source outside the cartridge half or cassette half (for example, vibration caused by operation of motor) exerts baneful influence on recording and reading-out, so that it is difficult to have accurate recording and reading-out of information. Therefore, the damping material used as a structural material for cartridge half or cassette half is strongly required to satisfy the above requirement, i.e., to have an excellent internal loss at around room temperature while maintaining high strength and hardness.
As binder resin for damping material, there are usually used thermoplastic resins (rigid resins) such as polypropylenes, polystyrenes, acrylonitrile-butadiene-styrene copolymers, polycarbonates, polyphenylene ethers, modified polyphenylene ethers and the like. These rigid resins are preferably used because of relatively low cost and excellent molding workability.
These rigid resins, however, are not satisfactorily excellent in internal loss at around room temperature.
Many attempts have been made for improving a damping property of these rigid resins. For instance, Japanese Patent Application Laid-open (KOKAI) No. 2-3-00250 proposes a polypropylene composition improved in a damping property obtained by incorporating a styrene-isoprene-styrene block copolymer in polypropylene resin. Japanese Patent Application Laid-open (KOKAI) No. 3-45646 proposes an ABS resin composition having improved damping property, obtained by incorporating a styrene-isoprene-styrene copolymer to an acrylonitrile-butadiene-styrene copolymer. Japanese Patent Application Laid-open (KOKAI) No. 3-181552 proposes a polyphenylene ether resin composition having excellent damping properties, comprising a polyphenylene ether and a styrene-isoprene-styrene block copolymer. Japanese Patent Application Laid-open (KOKAI).No. 5-70699 proposes a thermoplastic resin composition with improved damping property, obtained by incorporating a styrene-isoprene-styrene block copolymer in a thermoplastic resin. Also, in Japanese Patent Application Laid-open (KOKAI) No. 5-59234 is proposed a damping material resin composed of polypropylene and a styrene-isoprene-styrene block copolymer.
More specifically, Japanese KOKAI No. 2-300250 discloses a polypropylene composition comprising (a) 97-50 parts by weight of polypropylene and (b) 3-50 parts by weight of a block copolymer having a number-average molecular weight of 30,000-300,000 or a hydrogenation product thereof, the said block copolymer composed of blocks (A) comprising an aromatic vinyl monomer having a number-average molecular weight of 2,500-40,000 and blocks (B) comprising isoprene or an isoprene-butadiene mixture, whose number-average molecular weight is 10,000-200,000 and 3,4 bond and 1,2 bond content is 40% or more, and which shows a peak of main dispersion of tan .delta. at 0.degree. C. or more.
The problem to be solved by Japanese KOKAI No. 2-300250 is to reduce vibration and noise at around room temperature in the range where various kinds of the equipments and appliances are practically used.
Japanese KOKAI No. 3-45646 discloses an ABS resin composition comprising (a) 97-50 parts by weight of an ABS resin and (b) 3-50 parts by weight of a block copolymer having a number-average molecular weight of 30,000-300,000 or a hydrogenation product thereof, the said block copolymer composed of blocks (A) comprising an aromatic vinyl monomer having a number-average molecular weight of 2,500-40,000 and blocks (B) comprising isoprene or an isoprene-butadiene mixture, having a number-average molecular weight of 10,000-200,000 and a 3,4 bond and 1,2 bond content of 40% or more and showing a peak of main dispersion of tan .delta. at 0.degree. C. or more.
The object of Japanese KOKAI No. 3-45646 is to improve a damping property at around room temperature in the widely used ABS resin for damping material in various kinds of the equipments and appliances.
Japanese KOKAI No. 3-181552 discloses a polyphenylene ether resin composition comprising (a) 97-50 parts by weight of polyphenylene ether and (b) 3-50 parts by weight of a block copolymer having a number-average molecular weight of 30,000-300,000 or a hydrogenation product thereof, the said block copolymer composed of blocks (A) comprising an aromatic vinyl monomer having a number-average molecular weight of 2,500-40,000 and blocks (B)comprising isoprene or an isoprene-butadiene mixture, having a number-average molecular weight of 10,000-200,000 and a 3,4-bond and 1,2-bond content of 40% or more and showing a peak of main dispersion of tan .delta. at 0.degree. C. or more.
Japanese KOKAI No. 5-70699 discloses a thermoplastic resin composition comprising (a) 97-50 parts by weight of a thermoplastic resin and (b) 3-50 parts by weight of a block copolymer having a number-average molecular weight of 30,000-300,000 or a hydrogenation product thereof, said block copolymer composed of blocks (A) comprising an aromatic vinyl monomer having a number-average molecular weight is 2,500-40,000 and blocks (B) comprising isoprene or an isoprene-butadiene mixture, whose number-average molecular weight is 10,000-200,000 and Tg is 0 to 40.degree. C., wherein said blocks A and B are coupled together in the form of A(BA).sub.n or (AB).sub.n (n:an integer of 1 or more).
The object of Japanese KOKAI No. 5-70699 is to improve impact resistance in the low temperature region.
The thermoplastic resins proposed in Japanese KOKAI No. 5-70669 include polyolefins such as polyethylene and polypropylene, polyester such as polyethylene terephthalate and polybutylene terephthalate, styrene resins such as ABS and AS resins, polyamides, polyphenylene ethers, polyacetals and polycarbonates.
Japanese KOKAI No. 5-59234 discloses a damping material resin comprising a polypropylene resin composition composed of a mixture of 50-95% by weight of a polypropylene and 5-50% by weight of a thermoplastic elastomer and an inorganic filler, said inorganic filler being blended in an amount of 10-150 parts by weight based on 100 parts by weight of said resin mixture, wherein said thermoplastic elastomer is composed of a block polymer of a styrene-isoprene-styrene structure having polyisoprene blocks of vinyl structure.
A damping material composition obtained by adding iron oxide particles as an inorganic filler for improving a damping property is proposed in Japanese Patent Application Laid-open (KOKAI) No. 3-287652. The composition of this KOKAI comprises 100 parts by weight of a block copolymer having a number-average molecular weight of 30,000 to 300,000 and composed of blocks (A) comprising an aromatic vinyl monomer having a number-average molecular weight of 2,500 to 40,000, and blocks (B) comprising isoprene or an isoprene-butadiene mixture, having a number-average molecular weight of 10,000 to 200,000 and a 3,4-bond and 1,2-bond content of 40% or more and showing a peak of main dispersion of tan .delta. at 0.degree. C. or more, and 30 to 1000 parts by weight of iron oxide particles.
In production of damping materials mainly composed of thermoplastic resins, it has been common practice in the art to add an inorganic filler material directly to a base resin. However, for better handling and easier preparation of the composition, there is proposed a process using masterbatch pellets in which masterbatch pellets are prepared by dispersing an inorganic filler material in a base resin at a higher concentration than the desired one and these masterbatch pellets are mixed and dispersed in the base resin to adjust the concentration of inorganic filler to the purposed level thereof.
Accordingly, the masterbatch pellets for the damping material, which are easy to handle in producing the damping material and capable of affording a satisfactory damping effect with a moderate amount of addition thereof, are also required.
A damping material having an excellent internal loss in the commonly used temperature range, particularly at around room temperature (for example, 20 to 28.degree. C.), while maintaining a satisfactorily high strength and hardness of a rigid resin, is most strongly required at present, but none of the damping materials of the prior art mentioned above is unable to well satisfy the said requirements.
Any of the damping materials disclosed in the above-mentioned Japanese KOKAIs No. 2-300250, No. 3-45646, No. 3-181552, No. 5-70699 and No. 5-59234 is unsatisfactory in a damping property because of non-use of iron oxide particles as inorganic filler and also incapable of maintaining an intrinsic strength and hardness of a rigid resin because of high content of an inorganic filler.
The damping material disclosed in Japanese KOKAI No. 3-287652 mentioned above has an excellent damping property in the practical temperature range from room temperature to high temperature but is low in strength, that is, this damping material is low in bending modulus.
The problem to be solved by the present invention is to provide a damping material having an excellent internal loss in the practical temperature range, particularly at around room temperature, while maintaining the intrinsic strength and hardness of rigid resin.
As a result of the present inventors' earnest studies for solving the above-mentioned problem, it has been found that by preparing masterbatch pellets from 100 parts by weight of a binder resin composed of not more than 70% by weight of at least one base resin selected from the group consisting of polypropylenes, polystyrenes, acrylonitrile-butadiene-styrene copolymers, polycarbonates, polyphenylene ethers and modified polyphenylene ethers, and not less than 30% of styrene-isoprene-styrene block copolymer, and 50 to 300 parts by weight of iron compound particles, adding 70 to 99% by weight of at least one base resin selected from polypropylenes, polystyrenes, acryl onitrile-butadiene-styrene copolymers, polycarbonates, polyphenylene ethers and modified polyphenylene ethers to 1 to 30% by weight of said masterbatch pellets, and after kneading, molding the resultant mixture, the obtained damping material composed of 100 parts by weight of a binder resin composed of 85 to 99% by weight of at least one base resin selected from polypropylenes,. polystyrenes, acrylonitrile-butadiene-styrene copolymer, polycarbonates, polyphenylene ethers and modified polyphenylene ethers and 1 to 15% by weight of styrene-isoprene-styrene block copolymers, and 1 to 20 parts by weight of iron compound particles, has an excellent internal loss at around room temperature, and high strength and hardness. The present invention has been attained on the basis of this finding.